Partial pressure (Dalton's Law) Exercises Two containers are connected by a stopcock as shown on the left. Gas "A" is at a pressure of 202 kPa while gas "B" is at a pressure of 140 kPa. What will the resultant pressure be when the stopcock is opened? Step 1 Calculate the pressure that each gas alone will exert when the stopcock is opened. Since the temperature and amount of each gas is constant we use the formula below. P1V1 = P2V2 For gas "A" P1 = 202 kPa, V1 = 60L, P2 = ?, V2 = 100L, P2 = (202 X 60)/100 = 121.2 kPa. For gas "B" P1 = 140 kPa, V1 = 40L, P2 = ?, V2 = 100L, P2 = (140 X 40)/100 = 56 kPa. Step 2 add the individual pressures of each gas. Total pressure = P(A) + P(B) = 121.2 + 56 Total pressure = 177.2 kPa. Two containers are connected by a stopcock as shown on the right. Gas "A" is at a pressure of 402 kPa while gas "B" is at a pressure of 100 kPa. What will the resultant pressure be when the stopcock is opened? 25 litres of oxygen gas at 120kPa and 25 litres of nitrogen gas at 200 kPa are pumped into an evacuated(empty) 60 litre vessel. What is the final pressure of the 60 litre vessel if the temperature remained constant? Clues An 60 litre metal vessel contains carbon dioxide at 160 kPa and 23oC. A further 300 litres of nitrogen gas are pumped into this vessel at 140 kPa and 23oC. If the volume of the vessel and temperature remain constant what is the final pressure of the vessel? Answer A vessel containing 60L of hydrogen gas at 20oC and 100kPa pressure is connected via a valve to a 40L vessel containing oxygen at 20oC and 230kPa pressure. The valve is opened and both gases expand to fill the entire volume of both vessels. As the valve was opened both vessels were heated to 100oC. Calculate the partial pressure of each gas. Clues Answer

Home